U.S. patent application number 14/394392 was filed with the patent office on 2015-11-12 for method of manufacturing light emitting device.
The applicant listed for this patent is Michael A. Adamko, David J. Bravet. Invention is credited to Michael A. Adamko, David J. Bravet.
Application Number | 20150321387 14/394392 |
Document ID | / |
Family ID | 49328003 |
Filed Date | 2015-11-12 |
United States Patent
Application |
20150321387 |
Kind Code |
A1 |
Bravet; David J. ; et
al. |
November 12, 2015 |
METHOD OF MANUFACTURING LIGHT EMITTING DEVICE
Abstract
A novel method of producing an encapsulated light emitting
device. A preferred mold release film that can be used during the
encapsulation of a LED chip has an elastic modulus and a glass
transition temperature that are low enough as compared to the
desired molding temperature that the release film will closely
conform to the interior of the molding cavities used to form a
protective lens surrounding an LED chip. A preferred release film
according to embodiments of the present invention comprises a fully
fluorinated polymer, such as a perfluoroalkoxy polymer, including
MFA, or fluorinated ethylene propylene.
Inventors: |
Bravet; David J.;
(Westborough, MA) ; Adamko; Michael A.;
(Morristown, NJ) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Bravet; David J.
Adamko; Michael A. |
Westborough
Morristown |
MA
NJ |
US
US |
|
|
Family ID: |
49328003 |
Appl. No.: |
14/394392 |
Filed: |
September 4, 2012 |
PCT Filed: |
September 4, 2012 |
PCT NO: |
PCT/US12/53706 |
371 Date: |
April 20, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61623488 |
Apr 12, 2012 |
|
|
|
Current U.S.
Class: |
438/28 ;
425/436R; 428/141; 526/247; 526/254 |
Current CPC
Class: |
H01L 2224/48247
20130101; B29C 2045/1477 20130101; C08J 2327/20 20130101; H01L
2924/181 20130101; B29L 2011/0016 20130101; B29D 11/00807 20130101;
B29C 33/68 20130101; H01L 2224/48091 20130101; B29L 2031/34
20130101; H01L 2924/181 20130101; B29C 45/14016 20130101; H01L
2224/48091 20130101; B29C 2045/14155 20130101; Y10T 428/24355
20150115; C08J 2327/18 20130101; B29C 45/14639 20130101; B29C
37/0075 20130101; B29C 39/006 20130101; B29C 33/62 20130101; C08J
5/18 20130101; H01L 2933/005 20130101; H01L 33/54 20130101; H01L
2224/45144 20130101; H01L 24/97 20130101; C08J 2329/10 20130101;
H01L 2224/45144 20130101; H01L 25/0753 20130101; H01L 2924/00014
20130101; B29C 2045/0075 20130101; H01L 2924/00012 20130101; H01L
2924/00 20130101 |
International
Class: |
B29C 33/68 20060101
B29C033/68; C08J 5/18 20060101 C08J005/18; B29C 33/62 20060101
B29C033/62; H01L 33/54 20060101 H01L033/54; H01L 25/075 20060101
H01L025/075 |
Claims
1-49. (canceled)
50. A method of producing an encapsulated light emitting device,
the method comprising: providing a plurality of non-encapsulated
light emitting elements mounted on a support structure; providing a
mold having a plurality of cavities that define a shape of an
encapsulant to be formed around the light emitting element;
providing a release film covering the cavities, the release film
comprising a fully fluorinated polymer; conforming the release film
to the interior of the cavities; introducing a resin into the space
within the cavities, the release film preventing the resin from
contacting the interior of the cavities; positioning the
non-encapsulated light emitting elements so that they are within
the cavities and surrounded by the resin; curing the resin in the
space between the light emitting elements and the release film in
the cavities to encapsulate the light emitting elements; and
freeing the encapsulated light emitting elements from the mold and
the release film.
51. The method of claim 50 in which the light emitting device
comprises a light emitting diode (LED), a visible light LED, a
through-hole LED, a surface mount LED, a high-brightness LED, or an
organic LED.
52. The method of claim 50 in which the fluorinated polymer
comprises a perfluoroalkoxy polymer formed from polymerization of
at least tetrafluoroethylene (TFE) and perfluoromethyl vinyl ether
(PMVE).
53. The method of claim 50 in which the fluorinated polymer
comprises perfluoro methyl alkoxy (MFA) or fluorinated ethylene
propylene (FEP).
54. The method of claim 50 in which the fluorinated polymer has a
contact angle with water of at least 93 degrees.
55. The method of claim 50 in which the fluorinated polymer has an
elastic modulus at 150.degree. C. of no more than 50 MPa and a
glass transition temperature of less than 100.degree. C.
56. The method of claim 50 in which the fluorinated polymer has a
surface energy that is less than 25 dynes/cm.
57. The method of claim 50 in which the release film comprising a
fluorinated polymer has an average surface roughness of 0.20 .mu.m
or less.
58. The method of claim 50 in which the resin comprises a
heat-curable resin and in which the fluorinated polymer has a glass
transition temperature that is below the curing temperature of the
heat-curable resin.
59. A mold release film for use in manufacturing a light emitting
device, the mold release film comprising a fluorinated polymer film
having a glass transition temperature of less than 100.degree. C.;
an elastic modulus at 150.degree. C. of no more than 50 MPa.
60. The mold release film of claim 59 in which the fluorinated
polymer film has an average surface roughness of 0.20 .mu.m or
less.
61. The mold release film of claim 59 in which the fluorinated
polymer film comprises a fully fluorinated thermoplastic polymer
film.
62. The mold release film of claim 59 in which the fluorinated
polymer film has a contact angle with water of at least 93
degrees.
63. The mold release film of claim 59 in which the fluorinated
polymer film comprises a perfluoroalkoxy polymer formed from
polymerization of at least tetrafluoroethylene (TFE) and
perfluoromethyl vinyl ether (PMVE).
64. The mold release film of claim 59 in which the fluorinated
polymer film comprises perfluoro methyl alkoxy (MFA) fluorinated
ethylene propylene (FEP).
65. An apparatus for manufacturing a light emitting device, the
apparatus comprising: a mold having a plurality of cavities that
define a lens shape; winding reels for scrolling a mold release
film over the plurality of cavities; a dispenser for introducing a
silicone resin into the plurality of cavities; a vacuum system for
applying a vacuum to the plurality of cavities to form the release
film to the interior of the cavities; and a supply of a mold
release film, the mold release film comprising a roll of a fully
fluorinated polymer film.
66. The apparatus of claim 65 in which the light emitting device
comprises a light emitting diode (LED), a visible light LED, a
through-hole LED, a surface mount LED, a high-brightness LED, or an
organic LED.
67. The apparatus of claim 65 in which the fluorinated polymer
comprises a perfluoroalkoxy polymer formed from polymerization of
at least tetrafluoroethylene (TFE) and perfluoromethyl vinyl ether
(PMVE).
68. The apparatus of claim 65 in which the fluorinated polymer
comprises perfluoro methyl alkoxy (MFA) or fluorinated ethylene
propylene (FEP).
69. The apparatus of claim 65 in which the fluorinated polymer has
a contact angle with water of at least 93 degrees.
Description
TECHNICAL FIELD OF THE INVENTION
[0001] The present invention relates to manufacturing a light
emitting device and more particularly to the use of a mold release
film during the manufacture on an encapsulated light emitting
diode.
BACKGROUND OF THE INVENTION
[0002] A light emitting diode (LED) is a solid-state, semiconductor
light source having a number of advantages over more traditional
incandescent light bulbs and fluorescent lamps. Some of the
advantages of LEDs include low power consumption, small size,
faster on/off times, low heat radiation, long useful life, shock
resistance, and a simple fabrication process. Production of LED
devices continues to increase with increasing demand, partly driven
by utilization of LED devices in new applications.
[0003] A conventional LED generally comprises a semiconductor chip;
an encapsulant, often made of epoxy or silicone; and electrical
connection elements comprising two fine gold wires bonded to the
contacts and connected to two metal pins emerging from the
envelope. The semiconductor chip is doped to create a p-n junction
so that current will flow easily from the p-side, or anode, to the
n-side, or cathode, thus forming a diode. As current flows across
the diode, the movement of electrons and electron holes causes the
release of energy in the form of photons.
[0004] FIG. 1 is a diagram of a conventional LED, which includes
diode 102, having the structure described above, two external
electrodes 104 (connected to the cathode) and 106 (connected to the
anode), and an encapsulant 110, mounted on a substrate 112. The
encapsulant serves several functions, including protecting the
diode and electrical connections against oxidation and moisture,
improving shock resistance, and acting as a diffusing element or
lens for light produced by the LED.
[0005] A typical fabrication process is shown in FIG. 2, described
below, in which encapsulated LED devices are produced using
multi-cavity molds to form the encapsulating lens. Applicants have
discovered that the release film is a significant component with
respect to a variety of possible manufacturing defects for such
lenses. It is known to use ethylene tetrafluoroethylene (ETFE) film
as a mold release film for LED encapsulation. However, ETFE film is
available only from a limited number of suppliers. Further, not all
ETFE film is suitable for use as a mold release film.
[0006] What is needed is an alternative mold release film for use
during LED encapsulation and fabrication. Embodiments of the
present invention thus relate to a mold release film that meets the
requirements of industry in terms of yield and fabrication costs,
while also enlarging the range of products available for LED
fabrication.
SUMMARY OF THE INVENTION
[0007] A preferred embodiment of the present invention is directed
to a novel method of producing an encapsulated light emitting
device. A preferred mold release film that can be used during the
encapsulation of a LED chip has an elastic modulus and a glass
transition temperature that are low enough as compared to the
desired molding temperature that the release film will closely
conform to the interior of the molding cavities used to form a
protective lens surrounding an LED chip.
[0008] The foregoing has outlined rather broadly the features and
technical advantages of the present invention in order that the
detailed description of the invention that follows may be better
understood. Additional features and advantages of the invention
will be described hereinafter. It should be appreciated by those
skilled in the art that the conception and specific embodiments
disclosed may be readily utilized as a basis for modifying or
designing other structures for carrying out the same purposes of
the present invention. It should also be realized by those skilled
in the art that such equivalent constructions do not depart from
the spirit and scope of the invention as set forth in the appended
claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] For a more thorough understanding of the present invention,
and advantages thereof, reference is now made to the following
descriptions taken in conjunction with the accompanying drawings,
in which:
[0010] FIG. 1 is a diagram of a conventional prior art LED;
[0011] FIG. 2 shows a prior art method of forming encapsulated LED
devices using multi-cavity molds to form the encapsulating
lens;
[0012] FIG. 3 is a flow chart showing the steps in a method of
producing an encapsulated light emitting device according to
preferred embodiments of the present invention; and
[0013] FIG. 4 shows a prior art mold that could be used to practice
embodiments of the present invention.
[0014] The accompanying drawings are not intended to be drawn to
scale. In the drawings, each identical or nearly identical
component that is illustrated in various figures is represented by
a like numeral. For purposes of clarity, not every component may be
labeled in every drawing.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0015] Preferred embodiments of the present invention are directed
at a novel method of producing an encapsulated light emitting
device. A typical fabrication process for LED devices involves
encapsulating the LED itself within a dome-shaped lens of epoxy or
silicone. The encapsulating material, also referred to as potting
material, not only protects the LED from damage due to moisture,
shock, etc., the encapsulating material must also be adequately
transmit the desired wavelengths of light. The degree to which
light is transmitted by the encapsulant (lens) is an important
consideration in choosing an encapsulating material. Unfortunately,
some amount of the light generated by the LED chip will always be
trapped within the encapsulating material due to the refractive
index of the material and the degree of total internal reflection.
This trapped light undesirably reduces or otherwise alters the
light output of the LED device.
[0016] FIG. 2 shows a prior art method of forming encapsulated LED
devices using multi-cavity molds to form the encapsulating lens.
First, the prior art method comprises providing a plurality of
light emitting elements 201 mounted on a support structure 202,
such as an LED chip mounted on a PCB substrate. A mold with an
upper surface 205 and a lower surface 204 is also provided. Lower
surface 204 preferably has a plurality of cavities 206, with the
arrangement of cavities corresponding to the arrangement of LED
chips on the substrate. The shape of the cavities defines the shape
of the encapsulant or lens to be formed around the corresponding
light emitting elements. Typically, the cavities are shaped to
produce a dome-shaped lens, such as the one shown in FIG. 1. The
substrate, such as the PCB, is fixed in place (usually by
application of a vacuum) on the upper mold surface with the LED
chips facing the cavities in the lower half of the mold.
[0017] The cavities 206 are then covered by a flexible sacrificial
mold release film 208, which serves to prevent the encapsulating
material from adhering to the inside of the mold cavities, thus
allowing the mold to be re-used, and also to prevent damage to the
lens when the lens and mold are separated. The release film is
conformed to the inside of the cavities, usually by the application
of a vacuum through a vacuum pathway 210 in each cavity. Once the
vacuum is applied, the release film will be pulled into the
cavities to completely cover the interior surface of the cavities.
One common release film used in the prior art is formed from the
fluoropolymer ETFE. The release film can be supplied from a roll
212 of unused release film, with the used release film wound onto a
take-up reel 214.
[0018] Next, an encapsulating material 218 (also referred to as a
potting material) is introduced into the cavities. Typical
encapsulating materials include epoxies and silicone resin. Under a
partial vacuum, the LED chips or other light emitting devices 201
are then pressed into the encapsulating material so that the
encapsulating material 218 fills all of the space inside the
cavities 206. The mold is then clamped and heated (for example, to
100-150.degree. C. for 3-10 minutes) to cure the encapsulant
material. The mold can then be released and the encapsulated LED
devices 220 removed from the mold. The used release film can be
removed from the cavities, usually by winding the used film onto
the take-off roller 214 while a continuous portion of unused film
208 is rolled over the cavities so that the encapsulation process
can be repeated.
[0019] Molding equipment suitable for carrying out the process of
FIG. 2 is available, for example, from TOWA Corporation of Kyoto,
Japan; high-brightness LED chips are available, for example, from
Lextar Electronics Corporation of Hsinchu, Taiwan; and suitable
silicone resin for use as an encapsulating material is available,
for example, from Dow Corning of Midland, Mich., US.
[0020] Applicants have discovered that the release film plays a
surprisingly important role in the fabrication of encapsulated
light emitting devices, especially in regard to reducing
manufacturing failures and maintaining commercially acceptable
yields for the manufacturing process. Failures related to release
film can include peeling and/or crumbling of the lens surface after
demolding. In some cases, observed defects can include deformation
of the lens, sometimes referred to as a "cat-eye" defect because
the distorted lens shape often resembles a cat's eye rather than
the intended clear dome shape. These types of defects in
encapsulated LED lenses are seen even with prior art ETFE release
films. Such defects affect the light transmission of an
encapsulated LED and can render it unusable. Obviously, a high
yield rate (low incidence of failures) is very desirable from a
commercial standpoint.
[0021] Although such defects have long been observed during
encapsulated LED manufacturing, applicants now believe that the
source of these defects is poor conformity of the release film to
the mold cavity. Applicants have also discovered that
characteristics like tensile strength and dimensional stability
surprisingly do not appear to have a strong correlation to observed
lens defects. Instead, Applicants believe that the elastic modulus
and glass transition temperatures are more significant factors.
Applicants note, however, that although a theoretical basis for the
success of the invention is described herein, the invention has
been shown to work for the release film polymers described below,
regardless of the accuracy of the theory.
[0022] A preferred mold release film according to the present
invention will thus have an elastic modulus (E) at the mold
temperatures that is low enough for the preferred material to be
elastic enough to conform completely to the inside of the cavities.
A preferred mold release film will have an elastic modulus at
150.degree. C. of no more than 50 MPa, more preferably no more than
35 MPa, even more preferably no more than 30 MPa, and still more
preferably no more than 25 MPa. Additionally, a preferred mold
release film according to the present invention will have a glass
transition temperature (T.sub.g) that is low enough for the
material to have reached the rubber plateau, but not so low that
the material reaches its melting point. A preferred mold release
film will have a glass transition temperature of less than
100.degree. C., more preferably less than 90.degree. C., but with a
melting point above the highest operating temperature of the mold,
for example above 200.degree. C.
[0023] Additionally, Applicants believe that contact angle with
water is also a significant characteristic of a preferred mold
release film. Generally speaking, the higher the contact angle, the
lower the surface energy of the release film and the lower the
ability of the film to interact with or adhere to the encapsulant.
A preferred mold release film will have a contact angle of at least
93 degrees, more preferably of at least 95 degrees. The adhesion
forces between the release film and the encapsulant will also be
minimized by using a film having a lower surface energy. The
surface energy of ETFE, a commonly used release film for LED lens
manufacturing, is approximately 25 dynes/cm. A preferred release
film according to some embodiments of the present invention will
have a surface energy that is less than 25 dynes/cm, more
preferably less than 20 dynes/cm.
[0024] Although less significant from the perspective of solving
the problem of the previously unexplained encapsulation failures,
there are also a number of other characteristics that are desirable
for a release film according to the present invention. As an
example, a mold release film according to the present invention
preferably has a tensile strength of greater than 20 MPa and an
elongation-at-break at 150.degree. C. of greater than 200%. This
provides the mold release film with a sufficient amount of strength
and resiliency so that even when the film is deformed (as when it
in conformed to the interior of the cavities) cracking, tearing,
and overstretching can be prevented. Also, for the same reasons, a
preferred mold release film will be thick enough that the film will
be strong enough to avoid being unduly damaged during the
manufacturing process even where the tensile strength and
elongation-at-break are as described above. An example of a
suitable thickness would be at least 3 mils.
[0025] Finally, Applicants have also determined that it is
desirable that the mold release film have a surface that is as
smooth as possible in order to produce a lens having a surface that
is as smooth as possible. As discussed above, a rougher surface on
the LED lens can contribute to light scattering, which can reduce
the effectiveness of an LED light source. A preferred mold release
film will have an average surface roughness (Sa) of 0.20 .mu.m or
less, more preferably of 0.15 .mu.m or less, and even more
preferably of 0.10 .mu.m or less.
[0026] One exemplary group of materials that matches desired
characteristics discussed above and which could be formed into a
suitable mold release film would include certain fully fluorinated
thermoplastic polymers such as perfluoroalkoxy polymers,
specifically perfluoro methyl alkoxy (MFA). MFA comprises a
perfluoroalkoxy polymer formed from polymerization of at least
tetrafluoroethylene (TFE) and perfluoromethyl vinyl ether (PMVE).
With respect to the preferred characteristics described above, MFA
has an elastic modulus at 150.degree. C. of 17.3 MPa, and a glass
transition temperature of approximately 86.7.degree. C. Based upon
testing done by Applicants, a preferred mold release film formed
from MFA is capable of conforming very closely to the interior of a
mold cavity.
[0027] Another example of a suitable fully fluorinated
thermoplastic polymer would be fluorinated ethylene propylene
(FEP). With respect to the preferred characteristics described
above, FEP has an elastic modulus at 150.degree. C. of 48-50 MPa,
and a glass transition temperature of approximately 70.degree. C.
to 140.degree. C., depending on the exact resin being tested. Based
these values, a preferred mold release film formed from FEP would
also be capable of conforming very closely to the interior of a
mold cavity.
[0028] The following chart summarizes other relevant
characteristics of MFA and FEP (although measured values may vary
to some degree for different manufacturers or grades).
TABLE-US-00001 Contact Tensile Surface Energy Material angle Sa Tm
(.degree. C.) strength Elongation (dynes/cm) MFA 97.degree. 0.07
265-275 .sup. 21 MPa >300% (150.degree. C.) 17 (+/-0.01) 238%
(23.degree. C.) FEP 114.degree. Not available 265-275 20-26 MPa
390% (150.degree. C.) 16 350% (23.degree. C.)
[0029] FIG. 4 is a flow chart showing the steps in a method of
producing an encapsulated light emitting device according to
preferred embodiments of the present invention. The materials and
steps for practicing preferred embodiments of the present invention
are the same as for the prior art process described in FIG. 2 with
the exception of the novel mold release film used. In the method of
FIG. 4, the manufacturing operation begins in step 400. Next, in
step 401, a plurality of non-encapsulated light emitting elements
mounted on a support structure is provided. In preferred
embodiments of the present invention, an LED chip mounted on a PCB
substrate is used. The LED chip can be of any type or color.
Embodiments of the present invention are also suitable for use with
high-brightness LEDs. Although this method could be practiced using
a single light emitting element, in most cases a large number of
LEDs would be processed simultaneously.
[0030] In step 402, a mold having a plurality of cavities that
define a shape of an encapsulant to be formed around the light
emitting element is provided. Typically, the cavities will produce
a dome-shaped lens, such as the one shown in FIG. 1, but any
desired shape could be used. As with FIG. 2 above, the arrangement
of LED devices on the substrate should correspond to the
arrangement of cavities in the lower half of the mold so that each
LED can be placed in a separate cavity. The substrate, such as the
PCB, is then fixed in place (usually by application of a vacuum) on
the upper mold surface in step 403 with the LED chips facing the
cavities in the lower half of the mold. An example of the lower
portion of a mold 504 suitable for use with embodiments of the
present invention is shown in FIG. 5. Lower mold portion 504 has
cavities for forming two different sizes of LED lenses. For
example, larger cavities 550 could be used to form lenses having a
diameter of 2.5 mm, while smaller cavities 552 could be used to
form lenses having a diameter of 1.8 mm.
[0031] In step 404, a release film is provided and placed over the
cavities, a preferred release film according to embodiments of the
present invention comprising a fully fluorinated polymer, such as,
for example, a perfluoroalkoxy polymer, including MFA, or
fluorinated ethylene propylene. In step 406, the mold release film
is conformed to the inside of the cavities, preferably by was of a
vacuum pressure applied to each cavity that pulls the release film
down into each of the cavities. Next, in step 408, an encapsulating
material such as a resin (potting material) is introduced into each
of the cavities. In some preferred embodiments, the encapsulating
material can be injected into the cavities of the lower half of the
mold from a runner or nozzle. The release film fitting to the
interior walls of the cavities prevents the encapsulating material
from contacting the interior of the cavities.
[0032] In step 410, the light emitting elements are positioned so
that they are within the cavities and surrounded by the
encapsulating material. This can be accomplished by closing the
mold, which causes the light emitting elements (such as LED chips)
to be pressed down into the encapsulating material, thus causing
the encapsulating material to fill the cavities.
[0033] In step 412, the mold is then clamped and heated (for
example, to 100-150.degree. C. for 3-10 minutes) to cure the
encapsulant material. Once the cure is complete, in step 414, the
mold can then be released and the encapsulated LED device removed
from the mold. If additional LEDs are to be encapsulated 416, the
process returns to step 401; if not, the manufacturing process is
terminated in step 418.
[0034] A preferred embodiment of the present invention is thus
directed at a method of producing an encapsulated light emitting
device, the method comprising: [0035] providing a plurality of
non-encapsulated light emitting elements mounted on a support
structure; [0036] providing a mold having a plurality of cavities
that define a shape of an encapsulant to be formed around the light
emitting element; [0037] providing a release film covering the
cavities, the release film comprising a fully fluorinated polymer;
[0038] conforming the release film to the interior of the cavities;
[0039] introducing a potting material into the space within the
cavities, the release film preventing the potting material from
contacting the interior of the cavities; [0040] positioning the
non-encapsulated light emitting elements so that they are within
the cavities and surrounded by the potting material; [0041] curing
the potting material in the space between the light emitting
elements and the release film in the cavities to encapsulate the
light emitting elements; and [0042] freeing the encapsulated light
emitting elements from the mold and the release film.
[0043] According to another preferred embodiment, a method of
manufacturing a light emitting device including a light emitting
element encapsulated by a resin lens comprises: [0044] providing a
light emitting element mounted on a support structure; [0045]
providing a mold having a cavity that defines a shape of a lens to
be formed around the light emitting element; [0046] providing a
release film covering the cavity, the release film comprising a
perfluoroalkoxy polymer or fluorinated ethylene propylene; [0047]
conforming the release film to the interior of the cavity; [0048]
introducing a resin into the space within the cavity, the release
film preventing the resin from contacting the interior of the
cavity; [0049] positioning the light emitting element so that it is
within the cavity and surrounded by the resin; [0050] curing the
resin in the space between the light emitting element and the
release film in the cavity to form a lens encapsulating the light
emitting element; and [0051] freeing the light emitting device from
the mold and the release film.
[0052] According to another preferred embodiment, an apparatus for
manufacturing a light emitting device comprises: [0053] a mold
having a plurality of cavities that define a lens shape; [0054]
winding reels for scrolling a mold release film over the plurality
of cavities; [0055] a dispenser for introducing a silicone resin
into the plurality of cavities; [0056] a vacuum system for applying
a vacuum to the plurality of cavities to form the release film to
the interior of the cavities; and [0057] a supply of a mold release
film, the mold release film comprising a roll of a fully
fluorinated polymer film.
[0058] According to another preferred embodiment, a method of
producing an encapsulated light emitting device comprises: [0059]
providing a plurality of non-encapsulated light emitting elements
mounted on a support structure; [0060] providing a mold having a
plurality of cavities that define a shape of an encapsulant to be
formed from a heat-curable resin around the light emitting element;
[0061] providing a release film covering the cavities, the release
film selected from a group of fluorinated polymers having an
elastic modulus of 50 MPa or less at 150.degree. C., a glass
transition temperature that is below the curing temperature of the
heat-curable resin, a contact angle with water of at least 95
degrees, and a surface energy that is less than 25 dynes/cm; [0062]
conforming the release film to the interior of the cavities; [0063]
introducing a heat-curable resin into the space within the
cavities, the release film preventing the potting material from
contacting the interior of the cavities; [0064] positioning the
non-encapsulated light emitting elements so that they are within
the cavities and surrounded by the heat-curable resin; [0065]
curing the heat-curable resin in the space between the light
emitting elements and the release film in the cavities by heating
the mold to the curing temperature of the resin; and [0066] freeing
the encapsulated light emitting elements from the mold and the
release film.
[0067] In preferred embodiments of the present invention the light
emitting device can comprise a light emitting diode (LED), a
visible light LED, a through-hole LED, a surface mount LED, a
high-brightness LED, or an organic LED. Also, the resin or potting
material can comprise an epoxy or silicone.
[0068] In preferred embodiments of the present invention conforming
the release film to the interior of the cavities can comprise
applying a vacuum to the cavities through a vacuum port to fit the
release film to the interior of the cavities.
[0069] In preferred embodiments of the present invention the
fluorinated polymer can comprise perfluoro methyl alkoxy (MFA),
fluorinated ethylene propylene (FEP), and/or a perfluoroalkoxy
polymer formed from polymerization of at least tetrafluoroethylene
(TEL) and perfluoromethyl vinyl ether (PMVE). Also, the fluorinated
polymer can have a contact angle with water of at least 93 degrees
or a contact angle with water of at least 95 degrees. The
fluorinated polymer can have an elastic modulus at 150.degree. C.
of no more than 50 MPa, no more than 35 MPa, no more than 30 MPa,
or no more than 25 MPa. The fluorinated polymer has a glass
transition temperature of less than 100.degree. C. or less than
90.degree. C. and a surface energy that is less than 25 dynes/cm or
less than 20 dynes/cm.
[0070] In preferred embodiments of the present invention the
release film comprises a fluorinated polymer has an average surface
roughness of 0.20 .mu.m or less, an average surface roughness of
0.15 .mu.m or less, or an average surface roughness of 0.10 .mu.m
or less. The release film can also comprise a roll of fully
fluorinated polymer film, the fully fluorinated polymer having a
melting temperature of greater than 200.degree. C., a tensile
strength of 20 MPa or greater, and an elongation-at-break at
150.degree. C. of greater than 300%. In preferred embodiments, the
release film comprises a fully fluorinated polymer having an
elastic modulus at 150.degree. C. of no more than 50 MPa, no more
than 35 MPa, no more than 30 MPa, or no more than 25 MPa. In
preferred embodiments, the release film comprises a fully
fluorinated polymer having a glass transition temperature of less
than 100.degree. C. or less than 90.degree. C. The release film can
also comprise a fully fluorinated polymer having an average surface
roughness of 0.20 .mu.m or less, an average surface roughness of
0.15 .mu.m or less, or an average surface roughness of 0.10 .mu.m
or less. The release film can also comprise a fully fluorinated
polymer having a surface energy that is less than 25 dynes/cm or
less than 20 dynes/cm. In preferred embodiments the fully
fluorinated polymer comprises MFA or FEP.
[0071] Other preferred embodiments of the invention are directed at
a mold release film for use in molding a silicon lens to
encapsulate a light emitting diode in which the mold release film
comprises a fluorinated polymer film having a glass transition
temperature of less than 100.degree. C.; an elastic modulus at
150.degree. C. of no more than 50 MPa; and an average surface
roughness of 0.20 .mu.m or less. In preferred embodiments, the
fluorinated polymer film has a glass transition temperature of less
than 90.degree. C. The fluorinated polymer film can have an elastic
modulus at 150.degree. C. of no more than 35 MPa, no more than 30
MPa, or no more than 25 MPa. The fluorinated polymer film can have
an average surface roughness of 0.15 .mu.m or less, or 0.10 .mu.m
or less. The fluorinated polymer film can comprise a fully
fluorinated thermoplastic polymer film. The fluorinated polymer
film has a contact angle with water of at least 93 degrees, or of
at least 95 degrees.
[0072] In any of the embodiments described above, the fluorinated
polymer film can comprise a perfluoroalkoxy polymer formed from
polymerization of at least tetrafluoroethylene (TEE) and
perfluoromethyl vinyl ether (PMVE), perfluoro methyl alkoxy (MFA),
and/or fluorinated ethylene propylene (FEP). In some preferred
embodiments, the release film, as described in any of the specific
embodiments above, can have a thickness of no more than 3 mils.
[0073] Preferred embodiments of the present invention also include
a light emitting device made by any of the methods described
herein.
[0074] The invention described herein has broad applicability and
can provide many benefits as described and shown in the examples
above. The embodiments will vary greatly depending upon the
specific application, and not every embodiment will provide all of
the benefits and meet all of the objectives that are achievable by
the invention. Release film material suitable for carrying out the
present invention, such as MFA, is commercially available, for
example, from the assignee of the present application.
[0075] In the following discussion and in the claims, the terms
"including" and "comprising" are used in an open-ended fashion, and
thus should be interpreted to mean "including, but not limited to .
. . . " To the extent that any term is not specially defined in
this specification, the intent is that the term is to be given its
plain and ordinary meaning. The accompanying drawings are intended
to aid in understanding the present invention and, unless otherwise
indicated, are not drawn to scale.
[0076] Although the present invention and its advantages have been
described in detail, it should be understood that various changes,
substitutions and alterations can be made to the embodiments
described herein without departing from the spirit and scope of the
invention as defined by the appended claims. Moreover, the scope of
the present application is not intended to be limited to the
particular embodiments of the process, machine, manufacture,
composition of matter, means, methods and steps described in the
specification. As one of ordinary skill in the art will readily
appreciate from the disclosure of the present invention, processes,
machines, manufacture, compositions of matter, means, methods, or
steps, presently existing or later to be developed that perform
substantially the same function or achieve substantially the same
result as the corresponding embodiments described herein may be
utilized according to the present invention. Accordingly, the
appended claims are intended to include within their scope such
processes, machines, manufacture, compositions of matter, means,
methods, or steps.
* * * * *